Berlin 2008 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 9: Nonlinear dynamics, synchronization and chaos I

DY 9.4: Vortrag

Montag, 25. Februar 2008, 17:45–18:00, MA 004

Modelling of oscillatory phase separation of binary mixtures under continuous cooling — •Yumino Hayase, Günter K. Auernhammer, and Doris Vollmer — Max Planck Institute for Polymer Research, Mainz, Germany

We investigate the phase separation of binary mixtures under continuously ramping temperature using the Cahn-Hilliard equation including gravity. Our model is motivated by the experimental observation that for a broad range of composition and cooling rates binary mixtures may show pronounced oscillation in the turbidity, i.e. the transition to the biphasic state happens via a cascade of nucleation waves. The number of oscillations and their frequency depend on the choice of the components and the cooling rate [1]. Typically either the upper or the lower phase oscillates and hardly both. To understand the mechanism of oscillation instability we investigate the kinetics of phase separation under continuous cooling using the Cahn-Hilliard equation, the most widely studied model equation for the description of phase separation. To account for sedimentation we have added a mechanism to the C-H equation taking gravity into account. Numerically, we observe oscillatory wave of droplet formation. Depending on the composition and shape of the phase diagram, either both or only one phase oscillates. The oscillation period and the cooling rate have a power law relation. Experimental results support the numerical results very well.

[1] G.K. Auernhammer, D. Vollmer, and J. Vollmer, J. Chem. Phys., 123, 134511 (2005)